Many systems and mechanisms are known in which a component is movable between a closed or stowed position and an open or deployed position, and wherein a component should be locked in the desired position and unlocked to permit movement between the positions. Particular examples are valves or actuators, such as RAT actuators as described in more detail below.
Locking mechanisms are known to secure the actuator, valve etc. in a particular position, and unlocking mechanisms are known to release the locking mechanism and permit movement of the actuator/valve components to a different position, whereupon the actuator components can then also be locked in the second position by means of a locking mechanism. A locking mechanism for a RAT actuator is disclosed, for example, in US 2013/0327207.
Ram air turbines are used in aircraft to provide electric and/or hydraulic power to components of the aircraft, for example in the event of failure of other electrical or hydraulic power generating equipment on board the aircraft. In normal operation of the aircraft, the RAT is housed within the aircraft, but when needed it is extended into the airflow around the aircraft such that it may turn, due to the airflow, and generates electrical and/or hydraulic power. The RAT is typically pivoted into position by means of an actuator, for example a hydraulic actuator. The actuator typically includes a lock bolt which extends to deploy the RAT. The actuator has a lock mechanism which prevents inadvertent movement of the lock bolt and, thus, inadvertent deployment of the RAT. The main locking mechanism typically comprises a spring loaded lock bolt which must be moved in an axial direction to unlock the actuator. Such an actuator is disclosed, for example, in US 2015/0232195. RAT actuators are also disclosed in U.S. Pat. Nos. 8,640,563, 9,193,472 and US 2015/0096437.
An unlocking mechanism is provided to permit the axial bolt movement. A conventional unlocking mechanism is shown, for example, in FIGS. 2A to 2C, comprising a linkage arrangement, one end of which is rotatably coupled to one end of the lock bolt and the other end of which is axially fixed and rotatably coupled to, for example, a mounting wall. A solenoid moves the link between a locked (FIG. 2A) and an unlocked (FIG. 2B) position. In the locked position, the linkage assembly pushes against the lock bolt against the force of the lock bolt spring to prevent axial movement of the lock bolt. The assembly is in an over-centred position held by a spring and the lock bolt force. When it is required to deploy the RAT, the lock bolt needs to be released for axial movement of the actuator. As seen in FIG. 2B, a pull force, greater than the spring force, is exerted on the linkage assembly by means of a solenoid, which moves the linkage assembly to an under-centred position and out of engagement with the lock bolt. This allows the lock bolt to move axially to initiate actuator unlocking to permit deployment. The solenoid must have sufficient force to displace the lock bolt against the force of the lock bolt spring and the linkages and joints require sufficient axial and radial space and may also be prone to wear or damage.
The size and weight of components is of particular concern in aircraft where there is a desire to use lighter and smaller components, whilst maintaining safety and reliability. In addition, the conventional mechanism has been found to have some vulnerability to inadvertent self-deployment or failure to deploy due to the fact that there is a very small distance between the over-centred position (FIG. 2A) and the under-centred position (FIG. 2B) of the cross-rod. Only a small force, therefore, is required to deploy the actuator and this could happen accidentally, due, e.g., to vibrations.
There is a desire, therefore, to provide a locking/unlocking mechanism for such systems to prevent/permit axial movement of a component such as a lock bolt, without the need for very large solenoids and a series of links and in a more compact arrangement, and in which there is a reduced risk of inadvertent deployment.